Viewer: fix positioning of openseadragon viewport on page

[rmontroy]

This is the line that needs to be fixed: https://github.com/VanAndelInstitute/virtual-slide-viewer/blob/cfe84ac5648cc274ba1cffa5aad934153f14fcb6/src/ImageView/css/style.css#L28

You can see the problem whenever you shrink the browser width low enough that the status buttons take up 2 rows.